Here's a fun fact for conspiracy theorists, history buffs and trivia mavens: In this week's episode of "The Americans," we learn that the passcode for opening the safe room of the counterintelligence section of the Federal Bureau of Investigation is 9331. Reverse those digits and you get 1339. As it happens, 1339 is the year when the walls around the Kremlin were built. Get it? The FBI is the reverse of the Kremlin.

Now, I can't say for sure whether the showrunners had this little detail in mind when they wrote the episode. But it wouldn't surprise me. Because along with the intricate plotting, realistic dialogue and fantastic acting, the attention to such details is what sets "The Americans," now in its fifth season on the FX network, apart from everything else on television.

This business of getting the background minutiae of the period exactly right, pioneered by "Mad Men," is now de rigueur for television shows set in the recent past. But nobody is as passionate about accuracy as Joe Weisberg, the former Central Intelligence Agency case officer who created "The Americans."

For the uninitiated, the show revolves around Philip and Elizabeth Jennings, a couple living comfortably in a suburb of Washington during the Reagan administration. They experience the usual run of domestic problems, particularly those that arise from raising two children in the era when strict parental authority is falling apart. They also have to go out at night a lot, supposedly to meet clients of their travel agency, but really because they are Soviet spies. They were born in the Soviet Union, but raised from an early age to pose as Americans. (Hence the title.)

Like "The Sopranos," the program demystifies and humanizes a subject usually dealt with as fantastic and absurd melodrama -- there the Mafia, here espionage -- by placing it within the confines of an otherwise ordinary family with otherwise ordinary problems. Elizabeth and Philip aren't Stepford Spouses. Their marriage began as a pose but has long since become the real thing, with all the ordinary ups and downs that one would expect after all these years.

The drama is often painful but never melo. Recently, the writers have wisely put the family's focus on their daughter Paige, who is growing uneasily and rebelliously into her teen years. Two seasons ago, she spited her atheist parents by joining an evangelical church. I cannot think of another television program that would have both come up with the idea and played it straight.

Still, I will confess that I particularly enjoy the period details. As regular readers know, I am a history buff. Anachronisms bother me enormously. Among the most admirable qualities of "The Americans" is the determination of the showrunners to get things right. And it's not just music and automobiles and clothing that change as time passes for the characters. Half the fun of watching is spotting the smaller things.

In the first season, set in 1981, FBI agent Stan Beeman, pressed by his boss to draw a conclusion from insufficient evidence, asks whether he should put on his Carnac the Magnificent hat. In an episode set early in 1982, the family is off to see "Raiders of the Lost Ark." In 1983, the show's characters pause with the rest of the country to watch the ABC broadcast of "The Day After."

In season 4 we see a box of Banana Frosted Flakes on the kitchen counter. The kids eat Jif peanut butter, and the grownups drink Miller beer. In season 2, the Jennings' young son Henry covets the Intellivision video game system. In season 3, he does a passable Eddie Murphy imitation after watching the comic do a "Mr. Robinson's neighborhood" skit on "Saturday Night Live." And according to one eagle-eyed observer (I missed this detail myself, and would not have been qualified to spot it), a character in the most recent episode is wearing a Debbie Gibson scrunchie.

The show also traffics accurately in then-current events. There are no fictional ticking bombs. We see the Soviets' fear of Ronald Reagan driving the spies to take ever-greater risks to steal American military technology. The Soviet occupation of Afghanistan generates both espionage and personal dilemmas. In season 2, terrified of ARPANET (and not exactly sure what it is), the Soviets decide to try to bug the network. The current season builds in part on the Soviet Union's increasingly desperate need for grain as the 1980s wore on -- and an accompanying paranoia about why exactly the Reagan administration is being so helpful.

The spycraft too is well done. Former U.S. intelligence officials praise the show's accuracy. Former Soviet spies agree. And here, too, "The Americans" strives to get the details right. The tranquilizer gun used in season 2 was not a reproduction: It was a vintage firearm used by spies in the early 1980s.

In season 4, a Soviet spy gets his hands on the plans for the Centaur-G, a rocket stage that NASA would indeed have been testing at the time, although the program would later be cancelled after the Challenger explosion. True, experts say that "The Americans" has far more violence than one would find among real spies. Weisberg, the show's creator, does not argue the point. But, as he points out, "The Americans" is not a documentary.

No, it isn't. It's a marvelously rich and intelligent drama. And as the current season proves, even in a world now chock full of what has come to be known as prestige programming, "The Americans" remains the best show on television.

Stephen L. Carter is the William Nelson Cromwell Professor of Law at Yale, where he has taught since 1982. Among his courses are law and religion, the ethics of war, contracts, evidence, and professional responsibility. His most recent book is The Violence of Peace: America’s Wars in the Age of Obama (2011). He is an author and Bloomberg View columnist.